1. Field of Invention
The invention relates generally to the field of oil and gas production. More specifically, the present invention relates to a system for buffering explosions produced during wellbore operations.
2. Description of Prior Art
Various operations are conducted in a hydrocarbon producing wellbore that generate an explosion and/or percussive pressure wave in the wellbore. Such operations include wellbore perforating, a back-off shot, roll shot, dry pipe shot, and cutting devices. Downhole cutting devices typically sever a tubular member where the portion of the member above the cut is removed. Perforating systems are used for the purpose, among others, of making hydraulic communication passages, called perforations, in wellbores drilled through earth formations so that predetermined zones of the earth formations can be hydraulically connected to the wellbore. Perforations are needed because wellbores are typically completed by coaxially inserting a pipe or casing into the wellbore. The casing is retained in the wellbore by pumping cement into the annular space between the wellbore and the casing. The cemented casing is provided in the wellbore for the specific purpose of hydraulically isolating from each other the various earth formations penetrated by the wellbore.
One typical example of a perforating system 4 is shown in FIG. 1. As shown, the perforating system 4 comprises one or more perforating guns 6 strung together to form a perforating gun string 3, these strings of guns can sometimes surpass a thousand feet of perforating length. Connector subs 18 provide connectivity between each adjacent gun 6 of the string 3. Many gun systems, especially those comprised of long strings of individual guns, are conveyed via tubing 5. Others may be deployed suspended on wireline or slickline (not shown).
Included with the perforating gun 6 are shaped charges 8 that typically include a housing, a liner, and a quantity of high explosive inserted between the liner and the housing. A controller or operator (not shown) at surface 9 sends a signal via the wireline 5 to initiate perforation detonation. When the high explosive is detonated, quickly expanding explosive gases are formed whose force collapses the liner and ejects it from one end of the charge 8 away from the gun body 14 at very high velocity in a pattern called a “jet” 12. The jet 12 perforates the casing and the cement and creates a perforation 10 that extends into the surrounding formation 2. The resulting perforation 10 provides fluid communication between the formation 2 and the inside of the wellbore 1. In an underbalanced situation (where the formation pressure exceeds the wellbore pressure) formation fluids flow from the formation 2 into the wellbore 1, thereby increasing the pressure of the wellbore 1.
Ballistic detonation within a wellbore 1 creates a pressure wave PW that travels through the wellbore 1. The ensuing shock and vibration of the pressure wave PW is sufficiently large damage to damage other downhole tools in the wellbore 1 or proximate to the ballistics device. In some instances, the pressure wave PW can push the ballistics device itself suddenly up or down within the wellbore.